There are seven detectives assigned to Metro's cold case unit.
With few or any leads to work with, their job is challenging. It can take its toll emotionally trying to bring a killer to justice, while a family pleads for closure.
It's a job they willingly take on.
The most infamous cold case involves the disappearance of 13-year-old Tabitha Tudors, she vanished in 2003 while walking to a bus stop from her East Nashville home.
Cold case detective Steven Jolley has worked the case for years.
"On the Tabitha Tudors case...many times I've gotten a tip and I felt, 'man this is it, I'm gonna finally find out what happened to her,' only to be disappointed."
Disappointed... but giving up is not part of being a cold case investigator. You work the puzzle, and you come across one lead that can crack a long dormant case wide open.
Cold case detective Curtis Hafley looks at it like a puzzle.
"You know there are the ones out there that do get solved with that lead, that builds to another, that just keeps going and gets you to that point, and that's the whole part of doing what we do."
This is one job that's not nine to five, and when you do leave for the day the work usually follows you.
"If you got a case that you're working on, whether it be a couple of weeks old or years old, I can be out mowing the lawn and something will pop in my head about what I need to do. You often think about it, you cant erase it from your mind," said Jolley.
Jolley says you have to have an understanding family, too.
"If you got kids, they're gonna ask questions of what you do...you have to be careful about letting your kids know the type of things that you do because the things that we do are not necessarily what you want your kids to even know about."
Bringing a killer to justice also means a family gets the closure they so desperately need.
A collage of pictures in Jolley's office is a constant reminder of why he works the cold case unit.
A young man, Tevin Scruggs was shot and killed. He was mistaken for someone else, a two-year-old case, that is now solved.
"It's one that sticks with me, got to know the family. Like in a lot of the cases, you have so much interaction with the family you almost feel like you're part of the family."